The use of multi-tone telephone dialing has become increasingly popular and has resulted in numerous means to decode dual tones. The known systems are generally complex and of limited use since they are wired by jumpers to be responsive to a specific, distinguishable code sequence of digits.
More versatile tone decoders are available, however they generally employ sophisticated, complex circuitry which severally limits the commercial acceptance of the systems.
U.S. Pat. No. 4,275,271 on "Sub-Miniature Radio Telephone Decoder" issued to Charles Soulliard on June 23, 1981 is exemplary of preprogrammed decoders which are set for one specific telephone code or series of digits and may only be changed through rearranging jumper wires via a procedure that is not easily accomplished by a user in the field.
U.S. Pat. No. 4,354,248 on "Programmable Multi-Frequency Receiver" issued to D. Conger et al on Oct. 12, 1982 is exemplary of decoding techniques which use a programmable means to set the number sequence to be decoded. Systems of this type are generally complex and although programmable, are not readily programmed by a user in the field.